Material handling system for vibratory mills

ABSTRACT

A material handling system for vibratory finishing or grinding mills into which are placed materials and abrasive media and wherein the materials are operated upon. In a finishing mill the materials are parts which are finished, polished, or deburred, and in a grinding mill the materials usually are chemicals which are reduced in size. The system includes a vibratory mill into which such materials and media are placed, a vibratory screen separator for separating the materials from media after completion of the operation thereon, a hoist pan for handling the media or material and media, and a jib hoist system for moving and positioning the pan. Media or material and media are loaded into the pan, and same is lowered to the top of the finishing machine causing the load to be evenly dumped into the finishing machine. After the finishing operation, the material may be moved or transported in any suitable manner to any further operation stage, and the media is returned to the hoist pan. A pan driving mechanism is provided for rotating the pan as the media is supplied thereto from the separator or mill such that the pan is evenly loaded. Several bottom-dumping pan configurations are disclosed which provide a relatively even discharge of the media into the mill when the pan engages the mill.

United States Patent [1 1 Strom 1 Jan. 28, 1975 MATERIAL HANDLING SYSTEMFOR VIBRATORY MILLS [75] Inventor: John R. Strom. Fullerton, Calif.

[73] Assignee: Sweco, lnc., Los Angeles, Calif.

[22] Filed: July 25, 1973 [21] Appl. No.: 382,375

Related U.S. Application Data [60] Division of Ser. No. 253,272, May 5,1972, Pat. No

3,810.585, which is a continuation of Ser. No. 825,860, May 19, 1969,abandoned.

Primary Examiner-Robert G. Sheridan Attorney. Agent, or FirmLyon & Lyon[57] ABSTRACT A material handling system for vibratory finishing orgrinding mills into which are placed materials and abrasive media andwherein the materials are operated upon. In a finishing mill thematerials are parts which are finished, polished, or deburred, and in agrinding mill the materials usually are chemicals which are reduced insize. The system includes a vibratory mill into which such materials andmedia are placed, a vibratory screen separator for separating thematerials from media after completion of the operation thereon, a hoistpan for handling the media or material and media, and a jib hoist systemfor moving and positioning the pan. Media or material and media areloaded into the pan, and same is lowered to the top of the finishingmachine causing the load to be evenly dumped into the finishing machine.After the finishing operation, the material may be moved or transportedin any suitable manner to any further operation stage, and the media isreturned to the hoist pan. A pan driving mechanism is provided forrotating the pan as the media is supplied thereto from the separator ormill such that the pan is evenly loaded. Several bottomdumping panconfigurations are disclosed which provide a relatively even dischargeof the media into the mill when the pan engages the mill.

5 Claims, 12 Drawing Figures MATERIAL HANDLING SYSTEM FOR VIBRATORYMILLS This is a division of application Ser. No. 253,272 filed May 5,1972, now US. Pat. No. 3,810,585, which was a continuation ofapplication Ser. No. 825,860, filed on May 19, 1969 and now abandoned.

Reference is made to copending application Ser. No. 825,86l filedconcurrently herewith in the name of James P. Denight and George A,Burgess entitled Driving Apparatus for Hoist Pan." now US. Pat. No.3,672,581, and copending application Ser. No. 825,862 filed in the nameof Bernard S. Reckseit and George S. Burgess entitled Hoist Pans andHoist Pan Handling Apparatus,"- now US. Pat. No. 3,697,000, both of saidapplications being assigned to the assignee of the present application.

The present invention relates to vibratory mills and more particularlyto a material handling system for such mills.

Although applicable to both finishing and grinding mills, the conceptsof the present invention will be described with reference to finishingmills. Various types of finishing mills have been in use for a number ofyears for finishing, polishing and deburring. An example of theconstruction of a mill of this type is disclosed in Podmore et al US.Pat. No. 3,100,088. This type of mill includes an annular bowl intowhich is loaded parts and abrasive media. Examples of such parts arecastings of metal, plastic parts, and so forth. The mill may include asource of vibratory energy such as that described in Meinzer US. Pat.No. 2,284,671.

Conventionally, the media or parts and media are loaded into the millmanually. This has been accomplished through the use of a rectangularmedia receptacle having an opening at one end and suspended fron anoverhead hoist. Usually, two men, one holding the front end of thereceptacle down while the other pushes the rear end of the receptacle upare necessary in order to redistribute the media load in the pan from acarrying to a pouring position. The mill operator must be present inorder to load the media into the mill, and into the receptacle so as toproperly distribute the media load in the receptacle to prevent unevendistribution thereof. It will be readily apparent that there are anumber of disadvantages to media handling in this manner, not the leastof which is the lack of ability to automate the operational stepsrequired, and the complete reliance upon the adeptness of the meninvolved. Also, media generally is handled by bucket conveyors fromwhich is is difficult to remove all media when it is desired to changeto a different media. Consequently, undesirable mixing of differentmedia can occur.

Accordingly, it is a principal object of this invention to provide a newmaterial handling system for vibratory mills.

Another object of this invention is to provide an improved materialhandling system employing a substantially round pan for evenlydischarging a full load of material into a vibratory mill.

Another object of this invention is to provide an improved materialhandling system employing a substantially round pan for evenlydischarging a full load of material into a vibratory mill.

Another object of this invention is to provide an improved materialhandling system for vibratory finishing mills and which is readilyadapted to be partly or sub- 1 stantially automated.

These and other objects and features of this invention will becomebetter understood through a consideration of the following descriptiontaken in conjunction with the drawings in which:

FIG. 1 is a perspective view of a material handling system for vibratorymills according to the present invention;

FIG. 2a is a simplified plan view of a drive arrangement for the roundhoist pan used in the system of FIG. 1;

FIGS. 2b and 2: respectively are plan and elevational views of the panand drive system;

FIG. 3 is a fragmentary view of an end of a stabilizer arm forsupporting the hoist pan;

FIGS. 4a through 4c illustrate in more detail an embodiment of a roundhoist pan having an opening bot tom for dumping material into thevibratory mill;

FIG. 5 is a partial view of another embodiment of a round hoist pan; and

FIGS. 6a through 6c illustrate a further round hoist pan embodiment.

Turning now to the drawings, FIG. 1 illustrates a media handling systemfor vibratory mills incorporating the concepts of the present invention,and includes a vibratory finishing mill 10 of conventional constructionhaving a toroidal chamber 11 into which parts and abrasive media areplaced and vibrated such that the parts are finished, polished,deburred, and so forth. This mill may be, for example, a MODEL FM-lOmill manufactured by SWECO, Inc. of Los Angeles, Calif. The abrasivemedia or, parts and media if desired, is handled by a round hoist pan 12which is supported, moved and positioned by a stabilizer arm 13 of a jibhoist or bridge crane system 14. The pan 12 is moved and centered abovethe machine 10 to dump the load within the pan into the bowl 11. Afterthe finishing operation is completed, the parts and media are dischargedthrough a chute 15 into a vibrating screen separator 16 to separate theparts from the media. If the parts are of a metal suseptible to magneticattraction, a moving belt magnetic separator 17 may be used to retrievethe parts rather than allowing them to discharge from an end 18 of theseparator 16. The separator 16 includes a media discharge chute 19 forallowing the media to be returned to the pan 12 when it is moved to thedotted line position 20 as seen in FIG. I. The separator 16 is ofconventional construction and includes a screen having a mesh size forallowing media to fall therethrough and into discharge chute 19, themesh size being small enough to retain the parts for movement thereof tothe discharge end 18 of the separator 16. Alternatively a mill havingits own separating means may be used without requiring the use of aseparate separator 16. 1

As will be described subsequently, a drive system 21 is provided torotate pan 12 when it is in the position 20 during discharge of themedia from the chute 19 to evenly distribute the media in the pan.Rotation of the pan during loading thereof causes the material fedthereto to be evenly distributed therein. Uneven distribution ofmaterial would cause the pan to hang unbalanced and create difficulty intransporting, positioning and dumping the pan, and discharge of materialinto the mill would be uneven. The drive system may be a friction drivesuch as a type employing a rubber surfaced wheel, but preferably is amagnetic drive system as described subsequently.

The separator 16 preferably includes different mesh screens such thatreusable media can be separated from broken or chipped media, the latterbeing discharged through a chute (not shown). After the pan 12 has beenreloaded with media from the separator 16, it may be suitably stored onthe floor, in a rack, stacked with other pans, or again discharged intothe mill with a I new load of parts. Additionally, the reloaded pan maybe discharged into another mill of the nature of the mill 10 by the jibhoist system 14, or by another hoist system such as a bridge cranesystem. Another pan with a different size or type media may be picked upby the jib hoist system 14 and used with the mill 10. Thus, it will beapparent that various combinations of pans, media types and sizes,mills, and so forth may be incorporated into the system of FIG. 1.

Turning now to a more detailed discussion of the apparatus illustratedin FIG. 1, the finishing mill 10, as noted earlier, is a conventionalunit. This mill 10 includes a base 25 from which is supported the bowl11 by resilient members, such as springs (not shown). A vibratory sourceis mounted within the mill and coupled with the bowl to vibrate thesame. The bowl includes a center column 26 which has been modified toinclude a cover 27 having a projection 28. The projection, as will bedescribed subsequently, serves to open the bottom of the pan 12 to causedischarge of the material contained therein evenly into and around theinterior of the bowl 11.

The jib hoist system 14 includes a stationary base 30 which is freestanding or affixed in any suitable manner to the base 25 of the mill,such as by a pair of plates' welded to both bases, or affixed to theseparator base. The base 30 is provided with a vertical pivot or kingpin 31 which supports a vertical column member 32 of the crane forrotation to allow proper positioning of the pan 12. A horizontal beam 33is affixed to the upper end of the member 32 to support a hoist or winch34 by means of a hook 35. A counterbalance 36 may be provided. A chain37 is coupled between the winch 34 and a support bracket 38 on the outerend of the stabilizer arm 13. The bottom 39 of the bracket 38 has a slot40 therein perpendicular (note HO. 1) or angled (note FIG. 3) withrespect to the arm 13 for receiving and supporting the pan 12 as will bedescribed subsequently. The inner end of the arm 13 is coupled to a pairof flange members 43 and 44 which are coupled together by a pair ofplates and encircle the support member 32. Rollers are provided on theinner sides (note FIG. 2b) of these flange members to allow thestabilizer arm to roll up and down the member 32 as the winch 34 isoperated. A handle 45 is provided for rotating the hoist system aboutthe pivot 31 to allow the pan 12 to be moved to above the mill 10 or toanother closely adjacent mill, to be moved to the dotted line positionfor reloading the pan with media, or for moving the pan to anotherposition where it may be stored, stacked, or the like. The pan has adiameter slightly smaller than the inside diameter of the bowl 11.

The vibrating screen separator 16 may be a conventional unit including abase 50 which may be affixed to the base of the mill, and a screeningchamber 51. The screening chamber includes one or more screens and isvibrated by means of a motor and vibratory drive system 52. Thescreening chamber may include an upper coarse mesh screen for enablingthe parts to be separated from the media, and a lower fine mesh screento enable reusable media to be separated from broken and chipped media.The separatormay also include a suitable washing system (not shown) forwashing or treating the media and/or parts.v As noted earlier, thereusable media is discharged through the chute 19 into the pan. Althoughthe parts may be removed in any convenient manner from the upper screenof the separator, as noted earlier, a magnetic belt separator 17 may beemployed for picking up certain metallic parts.

Considering now the drive system 21 as more completely illustrated inFIGS. 2a through 20, the same includes an electrical motor coupled by achain 61 to a magnetic roller or rollers 62. An idler 63 maintainsproper tension of the chain 61. One or more of the rollers 62 may beprovided, and a typical roller if 4 inches in diameter. A metal wheel orpulley may be mounted on the motor shaft and directly contact and drivethe rollers 62 thereby obviating the need for a chain drive 61. Thisdrive assembly may be mounted to the overall system inone of-severalways. As illustrated in FlGS. 1 and 2a, a support bracket 64 may beaffixed to the base of the separator 16, or alternatively, may beaffixed to the base 30 of the crane or to the base 25 of the mill. Achannel member 65 as best seen in FIG. 2a is affixed to the'bracket64,'and has extending therefrom a pair of bracket plates 66 and 67.These bracket plates may in turn pivotally support a pair of bracketarms 68 and 69 for supporting the motor 60 and roller 62 at a pivot 70.A spring 71 is coupled between the arm 69 and the bracket 64, and stopplates 72 and 73 are respectively affixed to the arm 69 and bracket 64for aiding in release of the pan from the magnetic drive as will bedescribed subsequently.

The magnetic roller or rollers 62 serve two purposes. As the round pan12 is moved into position, the roller pulls the pan into engagementtherewith, and drives the pan. Typically, the pan is driven at a speedof 15 to 20 revolutions per minute to enable uniform distribution of themedia into the pan from the separator. As the pan is being loaded, thereis a tendency for the first gush of media to move the pan off center andaway from the driving roller 62, but this is overcome by the magneticattraction of the roller. Additionally, problems of friction andpressure in driving the pan are eliminated by the use of the magneticdrive. The pan may be separated from the roller by moving the panbackward (clockwise about the pivot thereby extending the retentionspring, and then pulling the pan forward briskly until the stop plates72 and 73 engage such that the momentum of the pan snaps it away fromthe roller. lf desired, discharge of parts or parts/media may be madedirectly from the finishing mill into the pan by physically rearrangingthe drive arrangement such that the pan is properly positioned withrespect to the mill for receiving the material therefrom.

FIGS. 2b and 2c illustrate an alternative arrangement for mounting thedrive assembly 21 wherein the channel member 65 thereof is pivotallysecured to the stabilizer arm 13. The drive assembly may be biasedclockwise as viewed in FlG. 211 by suitable means, such as a spring (notshown) to maintain the rollers 62 against the periphery of the pan 12.In the arrangement of FIG. 2b-2c, the bracket arms 68 and 69 are affixeddirectly to the channel member 65. It will be apparent that the rollers62 illustrated in FIGS. 1 and 2 are journalled for rotation by suitablebearings or bushings.

As noted earlier, the support bracket 38 of the stabilizer arm 13 has aslot 40 in the bottom thereof. This slot may have the configurationillustrated in FIGS. 2b and 3 wherein it flares outwardly at to enablethe support stud 76 (note FIG. 20) and flange 77 of the pan to be guidedinto engagement with the arm 13. The bracket may be in the form of a boxas shown in FIG. 1, or may be open as shown in FIGS. 2b, 2c and 3 withsides 78 and 79 and inclined faces 80 and 81 to guide and receive theflange 77.

FIG. 2b illustrates a flange 77 of one diameter for one size pan, andillustrates the manner in which the flange and support stud 76 may bepositioned in the support bracket 38 at the center line of thestabilizer arm 13. FIG. 3 illustrates the manner in which another sizepan having a larger flange 82 is supported and retained slightly offcenter. This support configuration enables different diameter pans to berotated by the magnetic drive arrangement. The chain 37 from the winch34 may be directly coupled with a hook 84 of the pan, or

alternatively, may be coupled near the outer end of the arm 13.

FIGS. 2b and 2c also illustrate in greater detail the manner in whichthe flanges 43 and 44 of the arm 13 are coupled together by means ofplates and 91 and include pairs of upper and lower rollers, only theupper rollers 92 and 93 being seen in thedrawings. These rollers bearagainst the faces of the column member 32 to allow the stabilizer arm 13to freely move up and down the member 32 as describedearlier.Additionally, a base plate 95 may be provided for supporting the base 30of the jib crane, and may also have secured thereto the bases of thefinishing mill and separator if desired.

Turning now to a consideration of the specific embodiments of the roundhoist pan 12, FIGS. 4a through 40 illustrate a pan 99 which includes alatching-type bottom 100 which is unlatched and caused to open as thebottom of the pan engages the top of the mill 10. This pan includes acylindrical housing or wall 101 with a bottom flange 102, and afrusto-conical insert 103 secured to the housing and flange. A centralcone 104 is provided and is secured at the top thereof by a plurality ofrods 105 extending to the interior wall of the body 101, and near thebottom thereof by a plurality of rods 106 extending to the insert 103.The bottom 100 of the pan 99 comprises a pair of semicircular bottomsegments 107 and 108 which are hinged together by a pin 109 whichextends through the bottom of the central cone 104. A flange 110 may besecured at the top of the housing 101 to reinforce the housing.

The bottom segments 107 and 108 are maintained in their normally closedposition by a pair of latch mechanisms, only the left hand mechanismbeing shown for simplicity of illustration. Each latch mechanismincludes a bolt 112 which releasably engages a bracket 113 affixed tothe respective bottom segment. The bolt is coupled to a release arm 114which is pivoted at 115 by a pair of brackets 116 and 117. As the bottom118 of the arm 114 engages a cam face 119 mounted at the top of the mill10, the bolt 112 is pulled from the bracket 113 allowing the respectivebottom segment to lower as illustrated in dashed lines in FIG. 4a. Thearm 114 is normally biased to close the bolt 112 with the bracket 113 bymeans ofa spring 121, and a spring 122 is provided to return the bottomsegments 107 and 108 to their closed positions after the media has beendumped from the pan 99. Latching mechanisms as just described areprovided for both of the bottom segments 107 and 108. It further will beapparent that the construction of the pan 100 dumps the media in asubstantially annular pattern into the interiorof the bowl 11 of themill 10 to provide a relatively even distribution of the media aroundthe bowl. No particular configuration is required at the top of thecenter column 26 to cause dumping of this pan embodiment.

FIG. 5 illustrates another round pan construction including acylindrical housing 130, a conical insert 131 and a pair ofsemi-circular bottom segments or doors 132 and 133. The central stud 76extends down into the pan and is coupled with the top of a cone 134. Acentral flange 135 is affixed to the inner wall of the housing 130 bymeans of a plurality of radially extending rods 136. A ball thrustbearing137 is provided, and FIG. 5 shows the configuration thereof whichis also used with the pan of FIG. 4a. The bottom segments 132 and 133are hinged by a pin 138 in a mannersimilar to the bottom segments 107and 108 in FIGS. 4a-4b; however, the hinge pin 138 is not coupled withthe cone 134, and the bottom segments 132 and 133 are free to move upand down with respect to the cone 134. Additionally, a pair of arcuateguides 139 and 140 are coupled at the inner circular edges of therespective bottom segments 132 and 133. when the cone 134 is in itslower position, the central portions of the bottom segments 132 and 133are supported thereon and the outer edges are supported on the insert131, and these segments assume the closed (full-lined) position. Theweight of the media on the segments maintains the bottom of the panclosed. The lower end of the stud 76 extends into :1 cylindrical guide141 in the cone 134, and the stud and cone are coupled together with apin 142. The pin 142 rides in a slot 143 in the guide. In this mannerthe cone may move freely up and down on the stud 76.

As the pan is lowered to the mill, the bottom of the cone 134 engagesthe cover 27 of the center column of the mill 10 thereby preventing thecone 134 from lowering further, while allowing the body 130 to lower tothe dashed lined position as seen in FIG. 5. This action allows thecentral portions of the bottom segments 132 and 133 at the guides 139and 140 to rise up with respect to the cone 134 because of the momentcaused by the weight of the media at the outer edges of the segments 132and 133 causing the segments to fold, thereby providing a substantiallyannular aperature 144 at the bottom of the pan for discharge of media.After the media is discharged, the pan is raised thereby allowing thecone to move down and the bottom segments to again assume the flatclosed position. If necessary, the bottom segments may be closedmanually.

Alternatively, the center column may include a remotely actuatedmechanism, such as an air cylinder and piston, which can be operated toextend upwardly and engage the actuator of the pan. With thisarrangement, the pan is merely lowered to above the mill and does nothave to be lowered into engagement with the cover 27.

FIGS. 6a through'6c illustrate another configuration of a round hoistpan providing an annular discharge of media. This pan includes a housinghaving a conical insert 151 affixed thereto, and a moving conical bottom152. The pan is supported by means of a central bracket 153 which issecured to the housing 150 by radially extending rods 154. A ball thrustbearing 155 is provided for the support stud 76, and the same type ofbearing is used with the pan of FIGS. 4a and 5. A central support column157 is rigidly secured to the interior wall of the insert 152 by meansof rods 158. The movable bottom 152 is affixed to a central cap 159which in turn is secured to a stud 160 which extends through the column157. A spring 161 is provided on the stud and is retained by means of anactuator 162 and nut [63. The spring 161 serves to normally bias theactuator 162 and stud 160, and thus the bottom 152, downwardly to thefull-lined position shown in FIG. 60. When the actuator 162 engages thecover of the center column of the mill, the bottom 152 is raised to thedashed-line position shown in FIG. 6a to provide an annular aperature165 for discharge of media evenly into the bowl of the finishing mill.The bottom of the actuator 162 is above the bottom of the pan thusenabling the pan to be placed on a floor for storage or loading withoutcausing the bottom 152 to open. With each of the pans disclosed herein,resilient gaskets may be used at the edges of the movable bottoms toprovide a good seal with the interior sides of pans.

It will be apparent that the present invention provides a new and novelmaterial handling system for vibratory mills wherein media or parts andmedia may be handled in a relatively simple, positive and efficientmanner, and may be evenly discharged into the finishing mill. The systemfurther enables the parts and media to be separated and the media to bereturned to the pan for subsequent storage and reuse. The presentinvention also provides a relatively simple construction for a roundhoist pan which can dump material contained therein into the finishingmill in a relatively evenly distributed manner. Furthermore, the systemof the present invention may be relatively easily automated through theuse of suitable controls and limit switches for sensing and controllingthe movement and positioning of the hoist pan.

As noted earlier, the concepts of the present invention also areapplicable to grinding mills wherein material, such as chemicalcompounds, paint pigments, and so forth, and media are loaded into themill to grind the material, or otherwise reduce the material in size.

What is claimed is:

l. A hoi'st pan for evenly dumping material into the chamber of avibratory mill comprising a substantially cylindrical housing, a centralcore member,

a plurality of arms interconnecting said housing and said core member,said central core member being freely supported by said plurality ofarms,

a pair of hinged bottom segments retained centrally on said core memberand retained at the outer edges thereof normally by said housing, saidsegment members being adapted to be released and folded downwardly fordumping the contents of said hoist pan, said bottom segments beinghinged together and freely mounted on said core member, said core memberbeing substantially frustoconical and tapering inwardly from the bottomthereof, the outer edges of said segment members normally being retainedby an inclined wall portion near the bottom of said housing, engagementof the bottom of said core member with said mill allowing said bottomsegment members to open by moving upwardly with respect to said coremember and pivotting to dump media into said mill.

2. A hoist pan for evenly dumping material into the chamber of a millcomprising a substantially cylindrical housing,

a support structure extending from a central position in saidsubstantially cylindrical housing to support said substantiallycylindrical housing,

a core member, said core member being mounted to said support structureto allow free vertical movement relative to said support structure, and

a pair of hinged bottom segments retained centrally on said core memberand normally extending outwardly to meet said substantially cylindricalhousing to close the bottom of the hoist pan, said core member beingconfigured to prevent movement of said core member upwardly through saidpair of hinged bottom segments, engagement of the bottom of said coremember with the mill allowing said hinged bottom segments to open bymoving upwardly with respect to said substantially cylindrical housingand pivotting to dump media into the mill.

3. The hoist pan of claim 2 wherein said support structure includes ahub, a plurality of arms extending from said hub to said substantiallycylindrical housing, and a vertical shaft extending through said hub,said core member being slidably mounted on said shaft.

4. The hoist pan of claim 2 wherein said substantially cylindricalhousing includes an inclined wall portion extending inwardly to meetsaid pair of hinged bottom segments.

5. The hoist pan of claim 2 wherein said core member is substantiallyfrusto-conical and tapers inwardly from the bottom thereof.

1. A hoist pan for evenly dumping material into the chamber of avibratory mill comprising a substantially cylindrical housing, a centralcore member, a plurality of arms interconnecting said housing and saidcore member, said central core member being freely supported by saidplurality of arms, a pair of hinged bottom segments retained centrallyon said core member and retained at the outer edges thereof normally bysaid housing, said segment members being adapted to be released andfolded downwardly for dumping the contents of said hoist pan, saidbottom segments being hinged together and freely mounted on said coremember, said core member being substantially frusto-conical and taperinginwardly from the bottom thereof, the outer edges of said segmentmembers normally being retained by an inclined wall portion near thebottom of said housing, engagement of the bottom of said core memberwith said mill allowing said bottom segment members to open by movingupwardly with respect to said core member and pivotting to dump mediainto said mill.
 2. A hoist pan for evenly dumping material into thechamber of a mill comprising a substantially cylindrical housing, asupport structure extending from a central position in saidsubstantially cylindrical housing to support said substantiallycylindrical housing, a core member, said core member being mounted tosaid support structure to allow free vertical movement relative to saidsupport structure, and a pair of hinged bottom segments retainedcentrally on said core member and normally extending outwardly to meetsaid substantially cylindrical housing to close the bottom of the hoistpan, said core member being configured to prevent movement of said coremember upwardly through said pair of hinged bottom segments, engagementof the bottom of said core member with the mill allowing said hingedbottom segments to open by moving upwardly with respect to saidsubstantially cylindrical housing and pivotting to dump media into themill.
 3. The hoist pan of claim 2 wherein said support structureincludes a hub, a plurality of arms extending from said hub to saidsubstantially cylindrical housing, and a vertical shaft extendingthrough said hub, said core member being slidably mounted on said shaft.4. The hoist pan of claim 2 wherein said substantially cylindricalhousing includes an inclined wall portion extending inwardly to meetsaid pair of hinged bottom segments.
 5. The hoist pan of claim 2 whereinsaid core member is substantially frusto-conical and tapers inwardlyfrom the bottom thereof.